Weird Openmp bug

Cheng_C_ — Tue, 04 Mar 2014 03:04:11 GMT

Dear all,

I want to combine OpenMP and RSA_public_encrypt and RSA_private_decrypt routines. However, I was confused by a weird bug for a few days.

In the attached program, if I generated 2 threads for parallel encryption and decryption, everything works well. If I generated 3 or more threads, the RSA_public_encrypt routine works fine. All strings are successfully encrypted (encrypt_len=256). However, the RSA_private_decrypt routine went wrong, that is, only one thread works properly, all the other threads failed to decrypt some of the strings (decrypt_len=-1, rsa_eay_private_decrypt padding check failed). If there are 1000 strings and 4 threads, the total number of string failed to decrypt went around 710 (some times as low as around 200). So as expected, if I use 4 threads for parallel RSA_public_encrypt and one thread for RSA_private_decrypt, nothing went wrong.

It would be great if you could give some ideas. Thanks very much.

#include <openssl/rsa.h>
#include <openssl/rand.h>
#include <stdio.h>
#include <string.h>
#include <omp.h>

#define KEY_LENGTH 2048
#define EN_SIZE 200 //number of chars in a string
#define STR_NUM 1000 //number of strings to be encrypted
#define PUB_EXP 3

int main() {

int i, j, k;
int encrypt_len;
int decrypt_len;

char *en_m[STR_NUM]; //array of pointers for the input strings
char *tm_m[STR_NUM]; //array of pointers for the encrypted strings
char *rm_m[STR_NUM]; //array of pointers for the encrypted strings
// rm_m read back tm_m through a .txt file
char *de_m[STR_NUM]; //array of pointers for the decrypted strings

// Generate key pair
RSA *keypair = RSA_generate_key(KEY_LENGTH, PUB_EXP, NULL, NULL);

FILE *f;
f = fopen("message.txt", "r");
if(f==NULL){
perror ("Error in locating the file to be encrypted");
return(-1);
}

for (k=0; k<STR_NUM; k++){
en_m = malloc(sizeof(char)*(EN_SIZE+1));
tm_m = malloc(sizeof(char)*(RSA_size(keypair)));
de_m = malloc(sizeof(char)*(EN_SIZE+1));
fread(en_m, 1, EN_SIZE, f);
en_m[EN_SIZE] = '\0';
}
fclose(f);
printf("The length of string to be encrypted in each encryption = %d bytes\n", EN_SIZE);
printf("Total number of the string message to be encrypted = %d\n", STR_NUM);

omp_set_num_threads(4); //set up 4 threads
kmp_set_defaults("KMP_AFFINITY=scatter");

// Encryption
#pragma omp parallel for shared(en_m, tm_m, keypair) private(i, encrypt_len) schedule(static)
for(i=0; i<STR_NUM; i++)
encrypt_len = RSA_public_encrypt(EN_SIZE, (unsigned char*)en_m, (unsigned char*)tm_m, keypair, RSA_PKCS1_OAEP_PADDING);
printf("Encryption has been finished\n");

f = fopen("en_message.txt", "w");
for (k=0; k<STR_NUM; k++){
fwrite(tm_m, sizeof(*tm_m), RSA_size(keypair), f);
}
fclose(f);

/************************************************************************************************/

f = fopen("en_message.txt", "r");
for (k=0; k<STR_NUM; k++){
rm_m = malloc(sizeof(char)*(RSA_size(keypair)));
fread(rm_m, 1, RSA_size(keypair), f);
}
fclose(f);

// Decryption
#pragma omp parallel for shared(rm_m, de_m, keypair) private(j, decrypt_len) schedule(static)
for (j=0; j<STR_NUM; j++)
decrypt_len = RSA_private_decrypt(RSA_size(keypair), (unsigned char*)rm_m, (unsigned char*)de_m, keypair, RSA_PKCS1_OAEP_PADDING);
printf("Decryption has been finished.\n");

int temp = 0;
for (k=0; k<STR_NUM; k++){
if (strcmp(en_m, de_m)!=0)
temp += 1;
}
printf("Total number of dismatch = %d\n", temp);

RSA_free(keypair);
for (k=0; k<STR_NUM; k++){
free(en_m);
free(de_m);
free(tm_m);
free(rm_m);
}

return 0;

}

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jimdempseyatthecove — Sat, 29 Mar 2014 16:43:47 GMT

You might find this pertinent: http://www.openssl.org/docs/crypto/threads.html#

Jim Dempsey

topic Weird Openmp bug in Intel® Moderncode for Parallel Architectures

Weird Openmp bug

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